1. Field of the Invention
The present invention relates to packaged semiconductors, semiconductor packages, leadframe assemblies therefor, and more particularly, but not by way of limitation, to semiconductor packages that can accept semiconductor chips of various sizes without having to change the footprint of the semiconductor package.
2. History of Related Art
It is conventional in the electronic industry to encapsulate one or more semiconductor devices, such as integrated circuit dies, or chips, in a semiconductor package. These plastic packages protect a chip from environmental hazards, and provide a method of and apparatus for electrically and mechanically attaching the chip to an intended device. Recently, such semiconductor packages have included metal leadframes for supporting an integrated circuit chip which is bonded to a chip paddle region formed centrally therein. Bond wires which electrically connect pads on the integrated circuit chip to individual leads of the leadframe are then incorporated. An encapsulating material, or encapsulant, which covers the bond wire, the integrated circuit chip and other components, forms the exterior of the package. A primary focus in this design is to provide the chip with adequate protection from the external environment in a reliable and effective manner.
As set forth above, the semiconductor package therein described incorporates a leadframe as the central supporting structure of such a package. A portion of the leadframe completely surrounded by the plastic encapsulant is internal to the package. Portions of the leadframe extend internally from the package and are then used to connect the package externally. More information relative to leadframe technology may be found in Chapter 8 of the book Micro Electronics Packaging Handbook, (1989), edited by R. Tummala and E. Rymaszewski, incorporated by reference herein. This book is published by Van Nostrand Reinhold, 115 Fifth Avenue, New York, N.Y.
Once the integrated circuit chips have been produced and encapsulated in semiconductor packages described above, they may be used in a wide variety of electronic appliances. The variety of electronic devices utilizing semiconductor packages has grown dramatically in recent years. These devices include cellular phones, portable computers, etc. Each of these devices typically include a printed circuit board on which a significant number of such semiconductor packages are secured to provide multiple electronic functions. These electronic appliances are typically manufactured in reduced sizes and at reduced costs, which results in increased consumer demand. Accordingly, not only are semiconductor chips highly integrated, but also semiconductor packages are highly miniaturized with an increased level of package mounting density.
According to such miniaturization tendencies, semiconductor packages, which transmit electrical signals from semiconductor chips to printed circuit boards and support the semiconductor chips on the printed circuit boards, have been designed to have a small size. By way of example only, such semiconductor packages may have a size on the order of 1xc3x971 mm to 10xc3x9710 mm. Examples of such semiconductor packages are referred to as MLF (micro leadframe) type semiconductor packages and MLP (micro leadframe package) type semiconductor packages. Both MLF type semiconductor packages and MLP type semiconductor packages are generally manufactured in the same manner.
One specific problem with the prior art is that chip sizes differ and/or increases due to different computing requirements of different products. With existing packaging design, fitting these larger chips means the packages must be made bigger. Bigger packages have larger footprints (the locations where the leads physically and electrically connect to printed circuit boards). The larger footprint forces the printed circuit boards to be redesigned for proper electrical connection. This redesign takes time and money. Thus, a semiconductor package that can fit circuit chips of different sizes without changing the semiconductor package""s footprint is needed.
The present invention relates to semiconductor packages that can accept semiconductor chips of various sizes without having to change the footprint of the carrier package. More particularly, one aspect of the present invention comprises a leadframe, a semiconductor chip attached to the leadframe, bond pads electrically connecting the semiconductor to the leadframe, and a sealing material. The leadframe has a plurality of leads, with each one of the plurality of leads having an upper side, a lower exposed side, and a laterally exposed side. The upper side of each one of the plurality of leads define a generally co-planar surface for supporting the semiconductor chip. Because the semiconductor chip rests on the co-planar and unobstructed surface defined by the upper side of the leads, semiconductors of different sizes can be attached to the semiconductor package without having to change the footprint of the semiconductor package. Finally, after sealing material encapsulates the components of the semiconductor package in a spacial relationship, the lower exposed side and the lateral exposed side of the plurality of leads are exposed to the outside surface of the semiconductor package.
Another aspect of the present invention is a leadframe that comprises a plurality of leads and a tie bar connecting to the plurality of leads. Each one of the plurality of leads has an upper side and a lower exposed side, with the upper side of each one of the plurality of leads forming a generally co-planar surface with the upper side of at least some of the leads. Further, when the tie bars are trimmed off the leadframe, they leave a lateral surface of the plurality of leads exposed to the lateral side of the semiconductor package.